This invention relates to improvements for in-mold polyurethane foam and/or resin products and the ability to provide surface coatings of such products exhibiting bright coloration and reduced colorant migration through utilization of easy-to-use polymeric colorants in simplified and environmentally friendly processing methods. The inventive surface coating formulations include polyurethane-reactive polymeric colorants admixed with prepolymer and excess amounts of certain isocyanate compounds. Such a composition is applied (by spraying, for example) to an internal composition, such as, preferably, mixtures of isocyanates and polyols (for the production of the internal polyurethane article) which is then introduced within a mold in order to form a particularly shaped or configured polyurethane article with a colored surface coating. Upon curing through exposure to heat, the coating composition reacts with the introduced polyurethane prepolymer to form a surface over the target internal polyurethane. The presence of excess isocyanate within the surface coating has been found to provide surprisingly good non-migration and non-bleed properties to the polymeric colorant thereby permitting the addition of such a highly desired, high color space, and effective polyurethane colorant within such surface coatings. The specific method as well as colored polyurethane articles are also contemplated within this invention.
In-mold polyurethane production has been practiced for many years in order to form thermoplastic or resinous articles of various shapes, sizes, and configurations. Such articles include, without limitation, novelty items, such as foam balls, seat cushions, automobile interior parts, such as steering wheel cushions and dashboards, and the like. Such products have generally consisted of internal polyurethane foam or resin and external coatings of either the same or different polyurethane formulations. In-mold processes have been developed and practiced to provide strong surfaces over the internal foam or resin in order to improve the quality of the molded article itself. Such a coating layer reduces surface defects such as sink marks, pores, microcracks and surface waviness to provide a more resilient polyurethane product.
Colored surface coatings are normally required to provide an acceptable appearance to the polyurethane article by masking the discoloration (yellowing) resulting from photochemical oxidation of bonded urethane during and after the in-mold curing process. Thus, for aesthetic reasons, both the internal and external compositions of such articles have been colored; however, different dyes and/or pigments have been required for both formulations due to the differences in processing and chemical constituents. Because of these differences, surface coatings have generally been prepared through the prior application of dyes, pigments, dyestuffs, or any combination thereof, to either the outer surface of the internal polyurethane or the mold surface itself. Traditionally, colored polyurethane coatings have been provided through the utilization of inorganic or organic pigments admixed with polyols to form a paste which is then coated over the mold surfaces within which the internal polyurethane prepolymer is then introduced. Upon curing, the coating attaches to the internal polyurethane to form the desired coated article. The selection of suitable dyes and pigments for this purpose is highly dependent on a number of qualities exhibited by such coloring agents, including dispensability, temperature stability, and migration stability in polyurethane.
Over and above such preliminary considerations is the fact that such dyes and pigments are difficult to handle in general as they are typically either provided in solid form, as powders (which contributes to breathing difficulties, etc., on an industrial level) or as dispersions. However, such dispersions are usually produced months prior to actual use and thus must be stored and transported. Due to the solid nature of such coloring agents, problems persist with the precipitation of such products over time that thus necessitates continued manipulation of the target dispersions by the user. As a result, the user must attempt to thoroughly mix the pigment dispersions prior to actual incorporation within the target articles. However, uniform stirring has proven difficult to attain which has invariably led to problems with uniform coloring of such polyurethane articles on an industrial scale. Additionally, due to the high staining characteristics of such dyes, pigments, etc., such past in-mold coloring procedures have required extensive cleaning steps if different colors are desired within certain molds, which may lead to higher costs of production. Furthermore, such pigments, dyes, etc., may also contain heavy metals which have proven to be environmentally taxing due to necessity of disposing of any excess coloring agents into groundwater, streams, and the like.
Although such dyes and pigments have proven to be relatively inexpensive, their performance as surface coating colorants has been unexceptional. For instance, the presence of solid particles has created specular reflectance problems which have resulted in the production of dull shades within the target coatings. Also, such particulate-containing coloring agents are generally difficult to thoroughly blend (if different pigments, dyes, etc., are mixed to produce different colors and/or shades) together, particularly in order to provide uniform colorations throughout entire batches of articles.
Polymeric colorants have been utilized in the past to possibly react with such surface polyurethanes to provide improvements in colorations. Such colorants, including those taught within U.S. Pat. No. 4,507,407 to Kluger et al., U.S. Pat. No. 4,751,254 to Kluger et al., U.S. Pat. No. 4,775,748 to Kluger et al., U.S. Pat. No. 4,846,846 to Rekers et al., U.S. Pat. No. 5,231,135 to Machell et al., and U.S. Pat. No. 5,864,002 to Stephens et al., all herein entirely incorporated by reference, do react with the urethane groups of the polymer to integrally become part of the polymer itself. However, such colorants are highly water soluble and have experienced problems with migration and bleed from such polyurethane surface coatings in the past. As such, loss of color over time and through simple frictional contact and/or atmospheric or liquid extraction have posed significant problems. Although such problems have persisted, there is a definite desire to utilize such colorants within polyurethane surface coating applications, primarily due to the ease of handling and storing of such liquid or waxy colorants over time (without precipitation problems or concerns); the ease in cleaning up after use due their high water solubility, greater flexibility through facilitating production of different colors and shades through simple mixing procedures as compared with dyes and/or pigments; and the environmentally friendly nature of such colorants due to their polymeric nature and thus high molecular weight.
As such, it has been of great desire to utilize such colorants within surface coating formulations for polyurethane articles. Unfortunately, the prior art has not accorded any improvements over the migration and color extraction as noted above for such colorants.
It is thus an object of this invention to provide a method of forming a colored polyurethane coating having a substantially smooth, brightly colored, aesthetically appealing surface. It is another object of this invention to provide a method of forming colored polyurethane coating for a polyurethane article with liquid, homogeneous colored polymeric colorants which exhibit substantially no migration, color loss, and/or color bleed problems over long-term use of the article. A further object of the invention is to provide an effective, aesthetically appealing, stable polyurethane colored surface coating without the need for heavy-metal containing compounds to provide such colorations.
Accordingly, this invention encompasses a colored polyurethane surface coating composition present over an article, preferably, though not necessarily, comprising a polyurethane resin or foam, wherein said surface coating comprises polymeric colorants, wherein the degree of coloration of colored polyurethane surface coating is retained after continued frictional contact and/or exposure to moisture. This invention also encompasses a composition of polymeric colorants admixed with from 1 to 3 times the amount of such colorants with an isocyanate compound selected from the group consisting of phenyl-based isocyanates and alkyl-based isocyanates. Further encompassed within this invention is a method of coloring a polyurethane surface coating of a polyurethane article comprising the steps of providing a polyurethane prepolymer composition; applying to the surface of such composition a formulation of polyurethane surface coating prepolymer further comprising a mixture of at least one polymeric colorant and (preferably, though not necessarily, from 1 to 3 times the amount of said polymeric colorant of) an isocyanate compound (preferably, though not necessarily, selected from the group consisting of phenyl-based isocyanates and alkyl-phenyl-based isocyanates); placing said coated polyurethane prepolymer within a mold; and curing said coated polyurethane polymer.